The present invention relates to improvements in disposable pipette tips and, more particularly, to an improved membrane filter pipette tip.
Use of pipette devices for the transfer and dispensing of precise quantity of fluid samples in analytical systems is well known as is the use of disposable pipette tip members for such pipettes. Disposable tips accommodate the serial use of such pipette devices in the transfer of different fluid samples without carryover or contamination.
Generally speaking, disposable pipette tips are formed of a plastic material and are of a hollow elongated tubular shape. An open proximal end of such pipette tips is designed to receive and releaseably mate with a lower end of a pipette tip mounting shaft of a pipette device while a distal end is of reduced cross section and includes a relatively small open end for passing fluids into and out of the pipette tip in response to operation of the associated pipette device.
It is often important that the fluid samples drawn into a pipette tip during aspiration operation of the associated pipette device not contact the mounting shaft or other internal components of the pipette device. To prevent such contact, it is common for disposable pipette tips to include a filter element tightly seated within the pipette tip at a location between the open proximal and distal ends of the tip. The filter member is intended to (i) freely pass air during the aspiration of fluid samples by an associated pipette device, and (ii) function as a barrier to aerosols in the fluid sample and to liquids which may be drawn into contact with the filter member as during "over pipetting".
For example U.S. Pat. No. 5,364,595 issued Nov. 15, 1994, describes a pipette including a filter member which is intended to function as a complete barrier to liquids. Unfortunately, during normal aspiration operations, such filter members have been found to function only as restricters of liquid flow and not as barriers to such flow.
U.S. Pat. No. 5,156,811 also describes a pipette tip including a filter member which is intended to function as a complete barrier to liquids. Unfortunately the type of filter material used within the filter member usually only acts as a complete barrier for a finite period of time and then allows liquid to pass therethrough. As described in the patent, the filter material is hydrophobic and includes particles of a hydrophilic material embedded in the pores of the hydrophobic filter material. Such particles sometimes dislodge from the filter material to contaminate the fluid sample during aspiration and dispensing operations of the associated pipette device. Further, if liquid sample contacts and is drawn into the pores of the filter material, such sample is often trapped within the pores of the filter material and will not dispense from the filter material during normal dispensing operation of the associated pipette. Such trapped sample is of unknown and varying quantity thereby introducing pipeting errors and nonreproducibility of pipeting results. Finally, removal of the trapped sample after the sample has contacted the filter member is difficult, time consuming and less than complete.
Accordingly, there is a continuing need for improved pipette tip including filter members which in practice allows air to freely pass therethrough while functioning as a barrier to the passage of liquids during normal fluid aspiration operation with pipette devices without trapping or contaminating any of the fluid sample.
Currently there are products known as membrane filter vents useful in medical devices which require fluids such as blood, urine, or intravenous solutions to flow in a sterile environment. Such membrane filter vents are inherently hydrophobic. They permit free passage of air while preventing the passage of aerosols and fluids such as blood, urine and intravenous solutions. When mounted in a pipette tip according to the present invention, it has been found that such membrane filter vents function as a filter material which will pass air while blocking the passage of liquids and aerosols thereby functioning as a true barrier to protect the mounting shaft and other internal components of pipette devices from contamination.